1. Field of the Invention
The present invention generally relates to a manufacturing method of a semiconductor device and a mask pattern forming method for forming a mask pattern included in the semiconductor device
2. Description of the Related Art
Patterns of wiring and separation width required in a manufacturing process tend to be miniaturized along with tendency of semiconductor devices to have higher integration. Such miniaturization is realized by forming a resist pattern using a photolithographic technique and etching a film to be etched which is various foundation thin films using the resist pattern as a mask pattern. In order to form the mask pattern, the photolithographic technique is important. The size in the recent miniaturization of semiconductor devices is required to be less than a resolution limit of the photolithographic technique.
So-called double patterning may be a method of providing the size less than the resolution limit of the photolithographic technique. The double patterning method is to form a mask pattern having a line width and a space width respectively narrower than a case where the mask pattern is formed with one patterning by providing patterning of two stages including a first mask pattern forming step and a second pattern forming step carried out after the first mask pattern forming step.
As one example of the double patterning method, there is known a method of forming a mask pattern having a pitch smaller than an original resist pattern array using a side wall patterning (SWP) method in which the film sidewall portions formed on both sides of a pattern are used as a mask. First, a photo resist film is formed to shape a resist pattern array in which line portions are arranged, and a silicon oxide film or the like is formed to isotropically cover a surface of the resist pattern array. Thereafter, the photo resist film is etched back to leave only the film side wall portions covering the side walls of the resist pattern array. Thereafter, the resist pattern arrays are removed. As a result, the silicon oxide films serving as the remaining film sidewall portions become a mask pattern as described in, for example, Patent Document 1.
However, when a mask pattern having a size smaller than the resolution limit of the photolithographic technique is formed by the method of SWP, there may be the following problems.
In the above mask pattern forming method, a bottom anti-reflecting coating (hereinafter, referred to as “anti-reflective coating film”) formed as a lower layer of the resist film used for photolithography is etched after forming the resist pattern array. By etching the anti-reflective coating film, the number of the processes increases and the cost may increase.
Further, it is preferable to enhance an etching rate (selected ratio) of the anti-reflective coating film with respect to the resist film when the anti-reflective coating film is etched. Therefore, it is impossible to use a hard material for the anti-reflective coating film, and the variety of the materials of the anti-reflective coating films is limited. Therefore, there may be a case where the production cost increases.
In order to facilitate etching of the anti-reflective coating film, it is impossible to increase the thickness of the anti-reflective coating film. Therefore, it is impossible to make the etched film, being the lower film of the anti-reflective coating film, function as a hard mask effective for etching the etched film, which is positioned lower than the anti-reflective coating film.
In the above mask pattern forming method, when the anti-reflective coating film is not etched, there may be a case where the silicon oxide film is formed to cover the resist pattern array, the film side wall portion of the silicon oxide film is left as the resist pattern array to etch back, and the pattern made of the film sidewall portion of the silicon oxide film is formed by removing the resist pattern array with ashing. However, when the resist pattern array is removed with ashing, there may be a case where the anti-reflective coating film exposed when the silicon oxide film is etched back is eroded with ashing. The anti-reflective coating film is eroded not only in the film thickness direction but also in directions parallel to the film surface of the anti-reflective coating film. Therefore, the mask pattern made from the film sidewall portion may fall down, referred to as so-called pattern collapse. [Patent Document 1] Japanese Laid-open Patent Publication No. 2009-99938.